This will probably seem heretical to you, but I was disappointed with Masterpiece Ultra Magnus. So many advances in TF engineering in recent years and yet they produce something that's got similar levels of articulation to the City Commander upgrade set. That one click available if you want to raise his arms to the side is lamentable, but you can get ONE MORE CLICK without modifying anything:
Rotate the arm forward 45° so that the white hinge joining the arm to the body lines up with the corner of the hole that houses the ratchet joint. Now you can go two clicks. You should be able to rotate the arm back to pointing straight down without un-clicking that joint.
This will probably get merged with the Ultra Magnus thread but the reason for posting it as a separate thread was because I figured not everyone is following the other thread. Did I use the word 'thread' enough in that sentence?